It has been widely recognized that Multi-view Video Coding (MVC) is a technology that serves a wide variety of applications including, for example, free-viewpoint and 3D video applications, home entertainment and surveillance. In those multi-view applications, the amount of video data involved is typically very large. Thus, there exists the need for efficient compression technologies to improve the coding efficiency of current video coding solutions performing simulcast of independent views.
Since a multi-view video source includes multiple views of the same scene, there exists a high degree of correlation between the multiple view images. Therefore, view redundancy can be exploited in addition to temporal redundancy and is achieved by performing view prediction across the different views.
In a practical scenario, multi-view video systems involving a large number of cameras will be built using heterogeneous cameras, or cameras that have not been perfectly calibrated. This leads to differences in luminance and chrominance when the same parts of a scene are viewed with different cameras. Moreover, camera distance and positioning also affects illumination, in the sense that the same surface may reflect the light differently when perceived from different angles. Under these scenarios, luminance and chrominance differences will decrease the efficiency of cross-view prediction.
Several approaches have been proposed for solving the illumination mismatch problem between pairs of images. In one such approach, hereinafter referred to as the first prior art approach, a scale/offset parameter for a 16×16 macroblock and predictive coding of these parameters may be used. Also, in the first prior approach, a rate-distortion cost based enabling switch may be used. However, the first prior art approach focuses on temporal video sequences. In video sequences, the illumination mismatch problem does not typically occur consistently as in cross-view prediction. In other prior art approaches, local illumination compensation methods for multi-view video coding are proposed, such as, for example, an approach in which an offset for each signal block is predictive coded and signaled in order to compensate the illumination differences in cross-view prediction.
May prior art approaches to illumination compensation use signaling bits to achieve illumination compensation. The signaled information will be able to better represent illumination mismatches, but the extra overhead in sending that information will penalize the benefit of gaining better prediction.